Loading system for long submarine cables



Feb. 11, 1930. B. F. LEWIS LOADING SYSTEM FOR LONG SUBMARINE CABLESFiled April 14. 1928 Patented Feb. 11, 1930 UNITED STATES PArENr orricaBENJAMIN F. LEWIS, OF BROOKLYN, NEW YORK, ASSIGIlTOR T0 AMERICANTELEPHONE AND TELEGRAPHCOMPANY, A CORPORATION OF NEW YORK LOADINGSYSTEM- FOR LONG SUIBMARINE CABLES Application filed April 14,

This invention relates to the artof communication over wires, and moreparticularly to an improved method for continuously loading a longsubmarine ocean cable designed for communication purposes. According tothis invention, the terminal portion of the cable is loaded to have thesame inductance per unit length as the central portion, using a greateramount of lower permeability material in order to reduce distortioneffects and impedance irregularities which otherwise tend to result fromthe use of high energy levels at the sending end of the cable.

In the drawing, Figure 1 shows a cross-section of a typical deep seasubmarine cable.

Fig. 2 shows asection of cable of the type shown in Fig. 1. In Fig. 2portions of the cable are cutaway to show the various layers of materialinvolved in building up the cable from the central conductor to itsouter covering. Fig. 3 discloses a cable sectioned along the line wm ofFig. 1. The cable of Fig. 3

discloses the improved loading system of the present invention.

Owing to the impossibility of amplifying signaling currents transmittedover a long submarine ocean cable at intermediate points along suchcable, it is desirable to employ a high energy level at the sending endto insure a level at the receiving end suificiently great that thesignals will not be rendered unintelligible in the presence ofinterfering currents introduced into the cable circuit from extraneoussources. If such a cable is continuously loaded at the ends in the sameman-- nor as is most economical for the principal portion, the highenergy level used at the sendingend may cause objectionable mag- 1928.Serial No. 270,164.

inductance resulting from the magnetic effects of large currents in theinitial portions of the cable. v

Large magnetic saturation effects cause signal distortion and otherobjectionable effects to be introduced in several ways. As a result ofnon-linearit between magnetizing current and resultant ux, which becomesgreater for the larger field intensities, extraneous voltages aregenerated and as a result, frequencies are transmitted to the receivingapparatus which were not present in the original signal current, andalso the original signal current may be altered in its relative mag-.

nitude. This efl'ect is generally termed asymmetric distortion. Besidesresulting in asymmetric distortion the large, non-linearity effect inthe, magnetic material would result in considerable intermodulation oftransmitted currents of different frequencies which would be detrimentalto the simultaneous operation of a multiple of transmission channelsover a loaded cable circuit. Distortion may result from the variation ininductance per unit length throughout the cable caused in the mannerdiscussed above. Large magnetic efiects would also increase thediificulty of equalizing the cable characteristics from the attenuationand velocity standpoints.

The variation in impedance in the initial portion of the cable, inaddition to causing refiection losses, would tend to reduce the balancewhich could be maintained between the cable and balancing networks whichmight Inorder to reduce the above detrimental effects to a satisfactorydegree the terminal portions of the cable may be loaded in a differentmanner from that employed for the 5 intermediate portion of the cable.It is proposed to do this and at the same time obtain the sameinductance per unit length for the terminal portions as for theintermediate portion of the cable by the use of a greater 1O amount ofloading material of such permeability as to give the same loading efiectas is obtained by the loading material of the intermediate portion. Theapplication of a different amount of loading material at the ter- 5minals might, of course, involve a graduation of several steps. In eachportion, however, y the relation between the permeability and the amountof loading material used would be adjusted so as to obtain the samecable induczo tance throughout.

Referring now to the drawing, the same elements are numbered alike inFigs. 1, 2 and 3. In Fig. 1, which shows in cross-section a typicalsubmarine cable embodying the improvements of the present invention, thecentral conductor, usually of copper, is indicated at 1. The loadingmaterial for the intermediate portion of the cable is indicated withinthe dashed circle 2. The loading material for the terminal portions ofthe cable is shown by the magnetic material 3. Surrounding the magneticmaterial is a layer of insulating material 4 which usually consists ofguttapercha. A return conductor 5, comprising a thin copper sheath,uniformly surrounds the insulating material ,4. In order to protect thecopper sheath 5 a layer of jute 7 is served about the outer coating ofthe sheath 5. In

' order to protectthe cable from injury due to 40 the rubbing action ofthe waves and the like a plurality of equally spaced steel armor wires 6are served helically about the cable throughout its entire length',-andthe steel armor wires 6 are covered'by another layer of jute 8, with thenet result that the armor wires become embedded in the cated in Fig. l.1

Referring now to Fig. 2 which shows a section' of cable; with variousportions cut away jute, as indito show the diflerent layers involved,the central conductor, usually of copper, is indicated again at ;1.Thcloading material used for. the principal and intermediate portion ofthey cable is shown at 2. This-loading material as indicated in Fig. 2consists of a ribbon of .magnetic material wound helically about thecentral conductor l 50 that it forms a continuous coating for the same.Any type of magnetic material might be adapted'in a certain instance,but it is probable that for any cable constructed at the present datepermalloy would be used. In Fig. 2 a single layer; of magnetic material2 is shown, but it to be understood, of course, that the lp'a'ding 2 aybe accomplished by windinga plu ality of thin ribbons over the conductorin such manner that a first ribbon would be wound about the conductorand a second ribbon would be wound about the first ribbon, and so on.This latter procedure would have the advantage of reducing thehysteresis and eddy current losses in the magnetic material.

The magnetic material for the terminal portions of the cable isindicated at 3, and again is shown to consist of a ribbon of magneticmaterial wound helically about the conductor. Here again, a plurality oflayers of magnetic material might be used, each layer comprising a thinribbon of magnetic material wound as indicated. The gutta-perchainsulating material surrounding the loading material is indicated at 4,the copper sheath at 5, the first serving of jute at 7, the steel armorwires at 6 and the last serving of jute at 8.

Referring now to Fig- 3, an entire cable is shown loaded in accordancewith the ideas set forth in the present invention. The cable is dividedinto three lengths A, B and C. In general, length A would equal lengthC. The numbering of the various elements in Fig. 3 is the same as forFigs. 1 and 2. In Fig. 3 it will be observed that the principal andcentrally located portion of the cable B is loaded to a given inductanceper unit length by uniformly distributing along the central conductor 1a giyen amount per unit length of magnetic material 2 of a predeterminedpermeability. The terminal portions of the cable A and C "are loaded tothe same inductance per unit length as the central portion by uniformlydistributing along the same about the central conductor a greater amountper unit length of magnetic material 3, having a lower permeability'thanthe material 2 used for the central portion of the cable. lVith a cabledesign such as suggested above, insuring approximately the 'same in-'ductance per unit length for the terminal and for the intermediateportions of the cable, the detrimental effects due to using a highenergy level at the sendingend of the cable can be reduced withoutintroducing the impedance irregularities. The use of an increased amountof loading material in the terminal portions of the cable will result inincreasing slightlythe external cable diameter. The effect of theincreased size of the conductor on the electrostatic capacity ofthecircuit can be offset by a compensating increase in the thickness of theinsulation. As in general the, liickness of the loading material is smaompared to the diameter of the conductor, the diameters of the loadedcond uetorsmnd the amount of insulating ma- 1.35 tei-talwill, however,be approximately the same throughout the cable.

What is claimed is: j

1. A submarine cable for communication purposes, the intermediateportion of which is continuously loaded to a given inductance per unitlength with a magnetic material of predetermined permeability and theterminal portions of which are continuously loaded to the sameinductance per unit length with a magnetic material of sufficientlylower permeability than that first mentioned to maintain the energylosses and frequency distortion due to the cable within predeterminedlimits based on the larger current flowing in the initial portion ascompared to that flowing in the remainder of the cable.

2. A submarinecable for communication purposes, the intermediate portionof which is continuously loaded to a given inductance per unit lengthutilizing therefor a magnetic materialof predetermined permeability, andthe terminal portions of which are continuously loaded to the sameinductance .per unit length utilizing therefor a magnetic material ofpermeability lower than that first men-.

tioned.

3. A submarine cable for communication purposes. comprising a centralconductor, loading material uniformly surrounding said conductor.consisting, for the intermediate portion of said cable, of a givenamount per unit length of magnetic material of a predetcrminedpermeability, said magnetic material being sufficient in amount to loadsaid portion of the cable continuously to a given inductance per unitlength, said loading material for the terminal portions of said cableconsisting of a sufficiently greater amount per unit length of magneticmaterial of permeability lower than that first mentioned to load theterminal portions continuously to the same inductance per unit length asthat of the intermediate portion and also to reduce the energy lossesand frequency distortion within said cable to a desired value based onthe larger current flowing in the initial portion as compared to that inthe remainder of the cable. a layer of insulating material uniformlysurrounding saidlloading material, a

' sheath of conductive material placed about said insulating material,protective layers of jute served about said conductive sheath, a

plurality of steel armor Wires served helically about said jute, and afinal layer of jute served about said armor wires.

4. In the art of electrical communication aver wires, the method ofreducing attenuation and distortion effects in a long submarine cablewhich consists in increasing the induc- April, 1928.

5, In the art of electrical communication over wires, the method ofreducing attenuation and distortion effects in a long submarine cablewhich consists in increasing the inductance of the terminal portions ofthe cable to a given value per unit length by uniformly distributingalong the same magnetic material of a predetermined permeability, andinthe two materials being so selected with reference to the increasedsignaling current flowing in the terminal cable portions compared tothat flowing in the intermediate portion that the distortion andattenuation effects are maintained within predetermined limits.

6. A long inductively loaded signaling conductor having a great overallattenuation in which the quantity per unit length and the permeabilityof the loading material are different on different sections but suchthat the effective inductance per unit length of conductor is the samefor all sections.

7. A long inductively loaded signaling conductor having a great overallattenuation in which the thickness and permeability of the loadingmaterial are different in different sections but such that the effectiveinductances of all sections are substantially the same.

8. Along signaling conductor having great overall attenuation. andsubstantially uniform diameter throughout, surrounded by magnetict'loading material, the magnetic characteristics of which vary with thedensity of the magnetic flux induced therein, characterized in this,that the quantity of magnetic material per unit length of conductor isgreater, but its permeability and variation of permeability withmagnetizing force are less on a section adjacent a terminal of theconductor than on a section more remote from the terminal, and furthercharacterized in that the product of the quantity of loading materialper unit length of conductor and the permeability of the loadingmaterial in each section of the conductor is the same as for every othersection.

9. A submarine cable conductor surrounded by one or more layers ofloading material characterized in that at least two of the threeparameters of the loading, namely the permeability, the number of layersand the thickness per layer are different indifferent portions of theconductor but in that the product of the number of layers, the thicknessper layer and the permeability is approximately constant for allportions of the conductor.

In testimony whereof, I have signed my name to this specification this12th day of BENJAMIN F. LEWIS.

